Monofilament yarn for a paper machine clothing fabric

ABSTRACT

A paper machine clothing (PMC) fabric includes a plurality of monofilament yarns, at least some of the monofilament yarns having a composition formed of polyethylene terephthalate (PET). The PET monofilament yarns have an abrasion resistance of greater than 6,000 cycles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a paper machine clothing fabric, andmore particularly, to monofilament yarns used in the paper machineclothing fabric.

2. Description of the Related Art

Polyethylene terephthalate (PET) is a polymer having good tensileproperties, processability and low moisture absorption. PET is usedextensively in apparel, home furnishings and industrial applications.Although PET has been utilized in the paper machine clothing (PMC)industry, due to the hostile conditions of the paper manufacturingprocess the mechanical life of PMC fabrics formed from PET is limited.During the operation of the papermaking machine the hostile conditions,such as mechanical stress, heat and moisture, work to break PETmonofilament yarns down, thus shortening the life of a fabric formedfrom such yarns.

Although efforts have been made to increase the life of PMC fabricsformed from PET monofilament yarns, each proposed solution to theproblem of low abrasion resistance has its disadvantages. For example,one approach to solving the problem of low abrasion resistance of PETmonofilament yarns was to use high molecular weight PET, as evidenced byEP 0 158 710 A1. Other efforts have involved the utilization of variousadditives to improve the physical properties of PET monofilament yarns,such as abrasion resistance. Each of these proposed solutions, however,requires expensive resin, expensive additives, and/or longer processingtimes which lead to higher production costs.

What is needed in the art is a PMC fabric and, more particularly, a PMCfabric yarn having improved or higher abrasion resistance, which is costeffectively produced without the need for additional additives orexpensive resin.

SUMMARY OF THE INVENTION

The present invention provides a paper machine clothing (PMC) fabricincluding a plurality of monofilament yarns, at least some of themonofilament yarns formed from polyethylene terephthalate (PET). The PETmonofilament yarns according to the present invention have an abrasionresistance of between approximately 6,000 and 20,000 cycles.

The invention in another form is directed to a paper machine clothing(PMC) fabric yarn for use in a PMC fabric. The PMC fabric yarn formedfrom polyethylene terephthalate (PET) and has an abrasion resistance ofgreater than 6,000 cycles, for example greater than 10,000 cycles orgreater than 15,000 cycles. The PMC fabric yarn formed from PET has anabrasion resistance of between 6,000 and 20,000 cycles.

The present invention further provides a method of manufacturing a papermachine clothing (PMC) fabric yarn for use in a PMC fabric including thesteps of: melting polyethylene terephthalate (PET); spinning the PETinto a filament; and drawing the filament into a monofilament PMC fabricyarn having an abrasion resistance of between 6,000 and 20,000 cycles.

An advantage of the present invention is the PET monofilament yarnsexhibit excellent abrasion resistance without the use of additives ormodifications to the molecular weight of the PET resin or therequirement of additional processing steps. Further, the increasedabrasion resistance results in a longer life expectancy of the yarnsand, thus, the fabric formed from the PET monofilament yarns.

An additional advantage of the PET monofilament processed according tothe present invention is that the maximum shrink force temperature ofthe PET monofilament is lowered. The lower shrink force temperature willenable a lower heat set temperature for spiral and woven fabrics whichshould result in lower energy and production costs.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a portion of a woven PMC fabricaccording to the present invention;

FIG. 2 is a partial schematic illustration of a spiral PMC fabricaccording to the present invention;

FIG. 3A is a schematic illustration of side view of a spiraledmonofilament yarn which may be used with the PMC fabric shown in FIG. 2;

FIG. 3B is an end view of the monofilament yarn shown in FIG. 3A; and

FIG. 4 is a flow chart of a method of manufacturing a PMC fabric yarnfor use in a PMC fabric according to the present invention.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate embodiments of the invention and such exemplifications arenot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there isshown a woven paper machine clothing (PMC) fabric 10 which generallyincludes a plurality of monofilament yarns 12. The PMC fabric 10 mayalso be in the form of a spiral fabric 10, which is illustrated in FIG.2. At least some of the yarns 12 are formed from polyethyleneterephthalate (PET) and have an abrasion resistance of between 6,000 and20,000 cycles. Other physical properties of the PET monofilament yarnsformed according to the present invention are similar to those of PETmonofilament yarns formed according to the state of the art.

Referring now to FIGS. 3A and 3B, there is shown one of the PETmonofilament yarns 12 according to the present invention. The inventivePET monofilament yarns 12 are converted into a shaped spiral yarn, asillustrated in FIG. 3A, using a thermomechanical process. Typically,this process takes place at elevated temperatures. According to thepresent invention, however, by lowering the process temperatures it ispossible to reduce the maximum shrink force temperature of themonofilament. Referring now to FIG. 3B, there is shown an end view ofPMC fabric yarn 12 which may be used with the PMC fabrics shown in FIGS.1 and 2.

PET monofilaments 12 according to the present invention may have adiameter between approximately 0.05 and 1.00 millimeters (mm), forexample 0.55 mm or 0.30 mm.

It is feasible to add an additive or multiple additives to improve, forexample, the chemical stability, hydrolytic stability or heat stabilityof the PET monofilament yarns. For example, Stabaxol® may be added tothe PET in order to improve the hydrolytic stability of PMCmonofilaments formed therefrom.

Referring now to FIG. 4, there is shown a flow chart of a method 14 ofmanufacturing PMC fabric yarn 12 according to the present invention.Method 14 according to the present invention generally includes thesteps of melting the polyethylene terephthalate (PET) (block 16);spinning the PET into a filament (block 18); and drawing the filamentinto a monofilament PMC fabric yarn having an abrasion resistance ofbetween approximately 6,000 and 20,000 cycles (block 20). Themonofilament formed in the drawing step (block 20) has, for example, amaximum shrink force temperature of equal to or less than approximately155° C.

The drawing step (block 20) of the method of the present inventionincludes the step of processing the monofilament in at least onerelaxation oven at a temperature less than approximately 320° F., forexample less than approximately 290° F. or less than approximately 250°F. This lower relaxation temperature during processing of the PMCmonofilament yarns, which is at least 30° F. less than the state of theart, yields an unexpected result in the form of improved abrasionresistance over PET monofilaments processed according to the known art.

EXAMPLE

The PET yarn was produced using the conditions listed in table 1. The0.72 IV PET resin was commercially available.

TABLE 1 Monofilament process conditions used to produce the sampleslisted in Table 2. Process Process Process Standard Modified PETModified PET Modified PET Parameter PET #1 #2 #3 Extruder Type SingleSingle Single Single Extruder Temperature - 530° F. 530° F. 530° F. 530°F. Zone 1 Extruder Temperature - 540° F. 540° F. 540° F. 540° F. Zones 2and 3 Extruder Temperature - 530° F. 530° F. 530° F. 530° F. Zone 4 DieTemperatures - All 530° F. 530° F. 530° F. 530° F. Zones Quench Tank140° F. 140° F. 140° F. 140° F. Temperature Oven #1 206° F. 206° F. 206°F. 206° F. Temperature Relaxation Oven #1 355° F. 248° F. 286° F. 320°F. Temperature Relaxation Oven #2 355° F. 248° F. 286° F. 320° F.Temperature 1^(st) Draw Ratio 4.35 4.35 4.35 4.35 2^(nd) Draw Ratio 1.161.16 1.16 1.16 3^(rd) Draw Ratio 0.95 0.95 0.95 0.95

Table 2 shows the comparison of the physical properties of the PETmonofilament yarns produced with a standard process and modifiedprocesses. The target diameter of the monofilament was 0.55 millimeter.ASTM D2256-97 method was used to carry out the tensile testing of theyarns. The test utilized to determine abrasion resistance consisted ofthe squirrel cage method, which includes a rotating drum of metal wireswhich are positioned perpendicular to the polymer strands. A pretension(load 500 grams for 0.55 millimeter diameter yarn and 350 grams for 0.30millimeter diameter yarn) is used on each polymer strand prior tostarting the drum. The metal wires on the rotating drum continuouslyabrade the strand and the number of cycles required to break the strandcompletely is quantified as an abrasion resistance of the yarn.

The maximum shrink force temperature of the monofilament is estimatedusing a Lenzing TST2 Machine. The yarn was mounted on the tester withone end fixed by a clamp and the other end pre-tensioned (0.01 gram perdecitex) before the other end of the yarn was clamped to maintain thepretension prior to the start of the test. The distance between theclamps in this case was 13 inches. The mounted yarn was heated on thetester in a closed environment from 50° C. to 240° C. with a heatingrate of 8° C. per minute. The development of the shrink force of theyarn was measured as a function of temperature by the machine. Thetemperature was then noted where the maximum shrink force value wasobserved on a shrink force curve. The maximum shrink force temperatureof the PET monofilaments according to the present invention is equal toor less than approximately 311° F. (155° C.).

TABLE 2 Comparison of yarn properties of standard PET and processmodified PET Standard Process Process Process PET Modified ModifiedModified 0.55 mm PET 0.55 mm PET 0.55 mm PET 0.55 mm Tenacity (g/den)4.08 3.85 3.93 3.95 Shrinkage (176° C./5 min) 13.3 17.6 17.6 14.6Elongation (%) 20.53 23.62 19.31 19.19 Abrasion Resistance - # of 5,00019,000 6,800 5,200 cycle to break Max Shrink Force (g) 491.0 616.4 302.9513.7 Max Shrink Force 330 265 300 310 temperature (° F.)

Example 2

The PET yarn was produced using the conditions listed in Table 3 below.The 0.95 IV PET resin was commercially available.

TABLE 3 Monofilament process conditions used to produce the sampleslisted in Table 4 below. Standard Process Modified Parameter PET PETExtruder Type Single Single Extruder Temperature - Zone 1 550° F. 550°F. Extruder Temperature - Zones 2 and 3 565° F. 565° F. ExtruderTemperature - Zone 4 565° F. 565° F. Die Temperatures - All Zones 565°F. 565° F. Quench Tank Temperature 140° F. 140° F. Oven #1 Temperature200° F. 200° F. Relaxation Oven #1 Temperature 370° F. 248° F.Relaxation Oven #2 Temperature 350° F. 248° F. 1^(st) Draw Ratio 4.104.10 2^(nd) Draw Ratio 1.30 1.30 3^(rd) Draw Ratio 0.94 0.94

TABLE 4 Comparison of yarn properties of standard PET and processmodified PET Process Standard Modified PET PET 0.30 0.30 mm mm Tenacity(g/den) 5.34 4.87 Shrinkage (176° C./5 min) 15.10 21.10 Elongation (%)17.01 19.18 Abrasion Resistance - # of 5,700 18,000 cycle to break

Table 4 shows the comparison of the physical properties of the PETmonofilament yarns produced with the standard process and with theinventive modified process. The target diameter of the monofilament was0.30 millimeter. Tensile properties and abrasion resistance of thesamples were measured by the same test methods as those described abovewith respect to Example 1.

While this invention has been described with respect to at least oneembodiment, the present invention can be further modified within thespirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

What is claimed is:
 1. A paper machine clothing (PMC) fabric including aplurality of monofilament yarns, at least some of said monofilamentyarns having a composition comprised of polyethylene terephthalate(PET), said PET monofilament yarns having an abrasion resistance ofgreater than 6,000.
 2. The PMC fabric according to claim 1, wherein saidPET monofilament yarns have a maximum shrink force temperature equal toor less than 310° F.
 3. The PMC fabric according to claim 1, furthercomprising at least one additive to improve at least one of a chemicalstability, a hydrolytic stability and a heat stability of said PETmonofilament yarns.
 4. The PMC fabric according to claim 1, wherein saidPET monofilament yarns have a diameter between approximately 0.05 and1.00 millimeters (mm).
 5. The PMC fabric according to claim 4, whereinsaid diameter between 0.10 and 0.70 mm.
 6. The PMC fabric according toclaim 1, wherein the PMC fabric is one of a woven fabric and a spiralfabric.
 7. The PMC fabric according to claim 1, wherein said PETmonofilament yarns are processed in at least one relaxation oven at atemperature less than approximately 320° F.
 8. The PMC fabric accordingto claim 7, wherein said temperature is less than approximately 290° F.9. The PMC fabric according to claim 8, wherein said temperature is lessthan approximately 250° F.
 10. A paper machine clothing (PMC) fabricyarn for use in a PMC fabric, said PMC fabric yarn having a compositioncomprised of polyethylene terephthalate (PET), said PET fabric yarnhaving an abrasion resistance of greater than 6,000 cycles.
 11. The PMCfabric yarn according to claim 10, wherein said PMC fabric yarn has amaximum shrink force temperature equal to or less than 310° F.
 12. ThePMC fabric yarn according to claim 10, further comprising at least oneadditive to improve at least one of a chemical stability, a hydrolyticstability and a heat stability of said PMC fabric yarn.
 13. The PMCfabric yarn according to claim 10, the yarn having a diameter betweenapproximately 0.05 and 1.00 millimeters (mm).
 14. The PMC fabric yarnaccording to claim 13, wherein the yarn has a diameter between 0.10 and0.70 mm.
 15. The PMC fabric yarn according to claim 10, wherein said PMCfabric yarn is processed in at least one relaxation oven at atemperature less than approximately 320° F.
 16. The PMC fabric yarnaccording to claim 15, wherein said temperature is less thanapproximately 290° F.
 17. The PMC fabric yarn according to claim 16,wherein said temperature is less than approximately 250° F.
 18. A methodof manufacturing a paper machine clothing (PMC) fabric yarn for use in aPMC fabric, said method comprising the steps of: melting polyethyleneterephthalate (PET); spinning the PET into a filament; and drawing thefilament into a monofilament PMC fabric yarn having an abrasionresistance of greater than 6,000 cycles.
 19. The method according toclaim 18, wherein the monofilament of said drawing step has a maximumshrink force temperature of equal to or less than approximately 310° F.20. The method according to claim 18, wherein said drawing step furtherincludes the step of processing the monofilament in at least onerelaxation oven at a temperature less than approximately 320° F.